Temporal covariation of egg volume and breeding conditions in the Common Kestrel (Falco tinnunculus) in the Mediterranean region

Most studies on variation in egg size in the Common Kestrel (Falco tinnunculus) have been carried out in central and northern Europe, whereas less is known about populations in the Mediterranean basin. We investigated the variation in egg volume in a Mediterranean population of Common Kestrel over a six-year period in relation to clutch size, breeding time, hatching success, and weather conditions. Eggs were generally bigger in larger clutches, and egg volume tended to decrease over the breeding season, but these patterns were not consistent among breeding seasons. Egg volume did not significantly vary in relation to weather conditions and did not predict hatching or fledging success. This study showed that (a) the patterns of covariation among laying date, clutch size and egg volume varied inconsistently over multiple years, and (b) egg volume poorly predicted the probabilities of hatching and fledging in the studied population.